The present invention relates to a fuel nozzle construction for use in gas turbine engines and, specifically, to a fuel nozzle utilizing water injection and which can be used with both gaseous and distillate fuels.
It is well known to inject water into the combustion chamber of a gas turbine engine. For example, in U.S. Pat. No. 2,847,825, there is disclosed a water injection system utilized to augment the thrust of an aircraft gas turbine engine for short periods of time, for example during take-off and other emergency conditions.
In U.S. Pat. No. 3,021,673, there is disclosed a water injection system for an automotive gas turbine for improving the acceleration characteristics of the engine.
In U.S. Pat. No. 4,044,549, a process is disclosed for providing low emission combustion gases wherein water is admixed with the fuel for the purpose of forming water vapor containing fuel droplets.
The utilization of water injection systems for substantially reducing NOx emissions is also disclosed in U.S. Pat. Nos. 4,110,973; 4,160,362; 4,259,837; 4,290,558; 4,337,618; 4,342,198; 4,519,769; and 4,600,151.
In the known water injection systems, water is typically injected from a position radially outwardly of the fuel, i.e., the atomized water is fed through the swirl vanes of the gas tip. However, experience has shown that this causes extreme thermogradients in the surrounding cap/cowl and combustion chamber liner assembly as a result of the direct impingement of the water on the hot component parts. The resultant thermal stresses create cracks and greatly reduce the useful life of the components, necessitating increased inspection frequency, maintenance and repair.
Previously, a solution to this problem has been attempted by substituting metal materials which are less prone to cracking, and by insulating the metals with thermal barrier ceramic coatings. While both of the above approaches have had limited success to the extent of extending the useful lives of the components, cracking still occurs.
This invention relates to an improvement over the conventional water injection techniques in that NOx emissions are reduced and the cracking problem associated with water injection is substantially abated. In accordance with this invention, the injected water is introduced directly into the flame center where it is more efficient at NOx control, and also eliminates direct water impingement on hot metals. The fuel nozzle of this invention also provides the capability of burning either gaseous or distillate fuel, utilizing water injection with both.
Preliminary tests of this concept have proven favorable. Specifically, water has been injected through the oil passage on a dual fuel style nozzle while running on gaseous fuel. Results show NOx levels have decreased, liner metal temperature gradients are more favorable, and dynamic pressure activity has remained acceptable.
In accordance with one exemplary embodiment of the invention, a fuel nozzle cartridge assembly including a water delivery pipe is provided for insertion into a central distillate fuel passage of a fuel nozzle body, from the rearward end of the body. This arrangement provides two separate and concentric passageways allowing pressurized water to be fed through the water delivery pipe and injected through the center of the nozzle body into the combustor as a finely atomized conical spray. Distillate fuel is fed through a side mounted inlet and travels through the annulus formed between the internal diameter of the body and the outside diameter of the water delivery pipe. The distillate fuel is injected into the combustor as a conical spray surrounding the water cone with atomization assisted by high pressure air introduced radially outwardly of the distillate fuel spray.
In the event gaseous fuel is to be burned, the distillate fuel passageway is shut down upstream of the nozzle body, and gaseous fuel is introduced into the combustion zone via a separate gaseous fuel passageway in the nozzle body. Water continues to be injected via the water delivery pipe within the distillate fuel passageway, and is again injected into the center of the flame.
In this exemplary embodiment of the invention, the water delivery pipe has an interior through passageway extending from a rearward open end to a forward open end. A mounting coupling is fixed to the exterior of the pipe adjacent its rearward end for use in mounting the cartridge assembly within the rearward end of the fuel nozzle body. A pipe fitting is also secured to the rearward end of the pipe for attachment to a water supply source.
The forward end of the cartridge pipe is provided with an interior water swirler and an exterior distillate fuel swirler, and the forward end of the fuel nozzle body is provided with an air swirler so that at the fuel nozzle tip, an outer conical air spray, an intermediate distillate fuel spray and an inner conical water spray combine to provide a homogenous mixture at the point of combustion.
In a broad aspect of the invention, therefore, a cartridge for supplying water under pressure to a fuel nozzle is provided which comprises an elongated tubular member having a discharge orifice at a forward end thereof, a coupling at a rearward end thereof, and a mounting element for securing the cartridge within a fuel nozzle body adjacent the rearward end.
In another broad but related aspect of the invention, a fuel nozzle for a gas turbine is provided which comprises a fuel nozzle body having gaseous fuel and distillate fuel discharge orifices at a forward end thereof, a tubular water feed cartridge assembly having a water discharge orifice at a forward end thereof; the elongated tubular water feed being concentrically mounted within a distillate fuel passageway of the nozzle body such that the water discharge orifice lies radially within the gaseous fuel and distillate fuel discharge orifices.
In still another related broad aspect of the invention, a method for reducing NOx emissions and for eliminating stress cracking in the combustion components of a gas turbine includes the steps of (a) injecting fuel into the combustion chamber of a gas turbine as a first conical spray; and (b) injecting water into the combustion chamber as a second, finely atomized conical spray located radially inwardly of the first conical spray so as to avoid direct water impingement on hot metal surfaces within said combustion chamber.
Additional objects and advantages of the present invention will become apparent from the detailed description of the invention which follows.